Organopolysiloxanes which contain at least one Si-bonded vinyloxy-functional group per molecule of the formula EQU H.sub.2 C.dbd.CH--O--G--
which G is an alkylene radical or represents an alkylene radical which is interrupted by a divalent hetero atom or a combination of hetero atoms, are known from U.S. Pat. No. 4,617,238 (published Oct. 14, 1986, J.V. Crivello et al., General Electric Company). Compositions which can be cross-linked by means of light and which contain the organopolysiloxanes mentioned above, and onium salts which catalyze the cationic polymerization of these organopolysiloxanes are described in U.S. Pat. No. 4,617,238.
The reaction of an organic compound containing four aliphatic double bonds, such as, for example, tetraallyloxyethane, with a silane containing Si-bonded hydrogen in the presence of a catalyst which promotes the addition of the Si-bonded hydrogen atom to an aliphatic double bond is described in U.S. Pat. No. 4,208,319 (published Jun. 18, 1980, P. August et al, Wacker-Chemie GmbH). Yields of organosilane containing 3 aliphatic double bonds of practically 100% of theory are obtained in this reaction. The organosilanes thus obtained are used as reinforcing additives in compositions which are based on organic polymers and fillers and can be crosslinked by means of sulfur or free radicals.
It is an object of the present invention to provide siloxane copolymers which contain alkenyloxy groups. Another object of the present invention is to provide a process for preparing siloxane copolymers containing alkenyloxy groups which allows for the introduction of more than one alkenyloxy group to a silicon atom. A further object of the present invention is to provide siloxane copolymers containing alkenyloxy groups which crosslink rapidly in the presence of light, especially ultraviolet light, to undergo cationic polymerization.